Most internal combustion reciprocating engines use pistons as a means of providing motive power. The pistons are each located in a cylinder, and are made air-tight by piston rings. Its purpose is to transfer force from expanding gas in the cylinder to the crankshaft by piston rods or connecting rods. The head of the piston is exposed to repeated bursts from compressed ignited gasoline and air in the cylinder, and therefore become worn with time and periodically require replacement. The pistons are connected to the piston rods by piston pins, and when the pistons are to be removed, the pins are pulled to allow the piston to be removed and then replaced by new or refurbished pistons.
Pistons currently come in two main varieties, the “full skirt piston” and the “short skirt piston”, also know as a “slipper piston”. FIGS. 1-2 show isometric views of the full skirt piston 20 with the major elements indicated. The piston assembly 1 includes a rod 2, which is attached to the piston 3 by a pivot joint 4 using a pin 5 (shown in both figures as being partially drawn). The pin 5 seats in a socket 6, which extends through the piston 3 into the rod 2, and back into the piston 3. The exterior of the socket 6 is referred to as the piston pin boss 7. The piston 3 includes rings 8 which seat in ring lands 9. The full skirt 21 extends down over the pin boss 7 and a portion of the rod 2.
FIGS. 3-4 show isometric views of the short skirt piston 30 and FIG. 5 shows a cut-away of the short skirt piston 30 with the major elements indicated. The major elements are referred to by the same reference numbers as when referring to the full skirt piston above, where appropriate, so again, the piston assembly 1 includes a rod 2, which is attached to the piston 3 by a pivot joint 4 using a pin 5. The piston 3 includes rings 8 which seat in ring lands 9. The pin 5 seats in a socket 6, which is surrounded by piston pin boss 7. The short skirt 31 can be compared to the full skirt 21 of FIGS. 1-2. It can be seen that the short skirt 31 is shorter on the sides than the full skirt 21, and extends only to just below the ring lands 9 at the front and back near the pin boss 7. It can also be see that the pin 5 is hollow and includes a pin bore 12.
The cross-sectional view of the short skirt piston 30 in FIG. 5 shows the pin 5 partially withdrawn from the socket 6 within the pin boss 7. Clips 10 are held in clip grooves 11 which are fashioned in the pin boss 7. These clips 10 serve to help retain the pins 5 in the pin bosses 7, and must be removed in order to remove the pins 5. The ring lands 9 are showed with the rings 8 removed.
Short skirt pistons are being used more and more commonly as a means of reducing internal friction in the cylinder and to reduce weight, both of which increase engine performance.
As the piston becomes worn, the piston pin boss often becomes deformed and sometimes includes burrs or other formations that resist the extraction of the pins. Thus, a considerable amount of force may be required to draw the pin and to allow the piston to be removed. Therefore piston pin puller tools have been devised to forcibly draw the pins. Prior piston pin pullers are generally configured for working with the traditional full skirt piston, and are fashioned with a sleeve that has a full circular end-section. This works well with the full skirt piston, where the end of the sleeve easily abuts the side of the skirt portion surrounding the pin socket. However, when this configuration is used with a short skirt piston, most of this skirt area surrounding the pin socket has been removed so that a sleeve with a full circular end-section does not rest evenly on the side of the piston.
As seen in FIG. 6 (prior art), the full circular end 42 of the pin puller sleeve 40 thus rests mainly on the area including portions of the piston ring lands 9. This can cause a number of problems, including damage to the rings and ring lands. If the ring lands are damaged the piston cannot be reused.
Also, since the circular end 42 of the prior art sleeve 40 is supported only at a portion of its circumference, which includes the skirt 31, but not the piston pin boss 7, when force 50 is applied to draw the pin 5, the sleeve 40 tends to pivot at this support point, resulting in a rotational moment 51. The pin 5 is thus not retracted in a straight line, but tends to also pivot. This can cause damage to the pin 5, and can gall the pin socket 6 as well.
Thus, there is need for a pin puller with a sleeve that conforms to the contours of a short skirt piston. Further, there is a need for a pin puller that has interchangeable sleeves that can accommodate both full skirt pistons and short skirt pistons.